I am on Android 5.1.1 and I am one of the ones reporting that Light Manager no longer works.
Today, though, I did something that may provide a clue to the problem. Perhaps McKoo is reading...
I just installed the latest version of Light Manager Pro on my S6 Edge. I then configured it to my preferences and rebooted the phone. As soon as the phone came up, I used my PC to send myself a text message. Now here is the important part. As soon as the text message was received, and before the alert notification took place, my LED started blinking according to the color and speed I configured in Light Manager for SMS messages (orange, every two seconds). However, as soon as the notification process alerted me to the text message (which I am assuming is a Samsung / Android process), my LED flashing reverted back to the standard blue flash every 5 seconds.
I sure hope the information above is helpful because I really like the Light Manager application. It provided the functionality that Android and Samsung forgot!